Peptides for Immune Support: What the Evidence Shows

Key Takeaways

• Compounds covered: Thymosin alpha-1, thymalin, thymulin, LL-37, BPC-157
• Goal area: Immune function, immune modulation, innate and adaptive immunity
• Evidence range: Ranges from 30+ clinical trials in 11,000+ subjects (thymosin alpha-1) to human longevity data from Russian clinical research (thymalin) to animal-only and in vitro data (LL-37, BPC-157)
• Regulatory range: None of the compounds discussed is FDA-approved in the US. None is currently permitted for compounding under Section 503A; LL-37 and BPC-157 are not available through licensed US prescribers at all.
• Key biomarkers for immune support: CBC with differential, hs-CRP, zinc, vitamin D, IGF-1, comprehensive metabolic panel
• As of April 2026: None of the compounds in this article are FDA-approved for any indication in the US, and none is currently permitted for compounding under Section 503A. BPC-157 was moved to a more restrictive posture following FDA's February 2026 reclassification, as reflected in the April 2026 bulk drug substances list revisions.
• Bottom line: Evidence quality varies widely across this category. Thymosin alpha-1 stands significantly apart from the other compounds by clinical trial scale. Zinc and vitamin D deficiency are among the most commonly identified modifiable contributors to impaired immune function and should be assessed before any peptide discussion.

Understanding Immune Support: The Biology

The immune system has two main functional branches that peptide researchers target through different mechanisms. The innate immune system is the first-responder layer — pattern-recognition receptors on neutrophils, macrophages, and epithelial cells detect and respond to pathogen-associated molecular patterns within minutes. Antimicrobial peptides like LL-37 operate within this system, disrupting microbial membranes and activating downstream inflammatory signaling.

The adaptive immune system is antigen-specific and memory-based. T lymphocytes — educated in the thymus — are the central adaptive effectors. CD4+ helper T cells coordinate immune responses by signaling to B cells and cytotoxic T cells; CD8+ cytotoxic T cells eliminate infected or malignant cells directly. The quality of adaptive immunity depends on the breadth of the T cell repertoire, which is established in the thymus and maintained through ongoing naive T cell output. Both thymalin and thymosin alpha-1 interact with this system, though through different mechanisms.

A third functional layer is immune regulation — the processes that prevent adaptive immunity from attacking self-tissues. Regulatory T cells (Tregs) suppress autoreactive responses. Thymosin alpha-1 is proposed to influence the balance between effector and regulatory immune responses; research has explored both immunodeficiency contexts (where effector responses are relevant) and inflammatory contexts (where regulatory balance is relevant).

Age-related immunosenescence — the progressive decline of immune function with aging — involves thymic involution, reduced naive T cell output, and accumulated memory T cells that occupy immune repertoire space without expanding the breadth of new responses. Thymic peptides are proposed to target the signaling environment that governs T cell maturation and output.

The gut-immune connection represents a fourth relevant pathway. A substantial portion of the body's immune cells reside in gut-associated lymphoid tissue (GALT). Intestinal barrier integrity affects systemic immune tone through microbial translocation and inflammatory signaling. BPC-157's proposed immune relevance is thought to operate through this pathway rather than through direct immunological action.

Peptides Studied for Immune Support: A Quick Comparison

The following peptides have published evidence relevant to immune function. They are listed by strength of available clinical evidence, from most-studied to least. Evidence level labels are mandatory disclosures, not marketing grades.

• Compound: Thymosin alpha-1
  Mechanism for immune support: Synthetic endogenous thymic peptide; promotes T-cell differentiation and maturation; modulates dendritic cell function; supports adaptive immune response while maintaining tolerance
  Evidence: 30+ clinical trials, 11,000+ human subjects across oncology, hepatitis B, hepatitis C, and immunodeficiency indications (predominantly in foreign-approval jurisdictions; these trials have not been accepted by FDA as establishing safety and efficacy for any US indication)
  FDA status: Not FDA-approved in the US; has regulatory approvals outside the US that FDA does not recognize; not on the FDA's Section 503A bulk drug substances list and not currently permitted for compounding
  SP availability: Not currently available through Superpower
  Route: Subcutaneous injection
• Compound: Thymalin
  Mechanism for immune support: Khavinson bioregulator; bovine thymus-derived polypeptide; activates haematopoietic stem cell differentiation; proposed tissue-specific epigenetic signaling for thymic restoration
  Evidence: Human longitudinal data from Russian clinical research including a 6-8 year observation; controlled study in 266 patients; methodological standards differ from FDA Phase 3 RCT requirements
  FDA status: Not FDA-approved in the US; Russian regulatory approval does not confer any US regulatory status; not on the FDA's Section 503A bulk drug substances list and not lawfully available through US compounding pharmacies
  SP availability: Not currently available through Superpower
  Route: Intramuscular injection in Russian clinical protocols
• Compound: Thymulin
  Mechanism for immune support: Endogenous zinc-dependent thymic nonapeptide; directly promotes T-cell maturation; declines with age and zinc deficiency
  Evidence: Extensive mechanistic physiology literature; zinc-correction human evidence; limited human therapeutic intervention data
  FDA status: Not FDA-approved as a therapeutic; not on the FDA's Section 503A bulk drug substances list and not lawfully available through US compounding pharmacies; no active US therapeutic development program for exogenous thymulin administration
  SP availability: Not currently available through Superpower
  Route: Endogenous; exogenous administration routes under investigation
• Compound: LL-37
  Mechanism for immune support: Endogenous human cathelicidin; antimicrobial membrane disruption; activates macrophage phagocytosis; modulates neutrophil inflammatory response
  Evidence: In vitro and animal studies only; no completed human clinical trials for therapeutic immune use
  FDA status: Not FDA-approved for any indication; no lawful US human-use pathway — a research peptide used in laboratory and preclinical studies
  SP availability: Not available through Superpower or any licensed prescriber for therapeutic use
  Route: Research studies — various routes; human therapeutic route not established
• Compound: BPC-157
  Mechanism for immune support: Gut cytoprotection; intestinal barrier restoration; anti-inflammatory signaling through the gut-immune axis
  Evidence: Animal studies only for immune applications; no completed human clinical trials
  FDA status: Not FDA-approved; not permitted for compounding under Section 503A following FDA's February 2026 reclassification, as reflected in the April 2026 bulk drug substances list revisions; FDA has identified significant safety concerns
  SP availability: Not available through Superpower
  Route: Oral or subcutaneous in animal studies; human route for immune applications not established

Compounds without a lawful US human-use pathway are not legal to prescribe, compound, or sell for human use in the US. Products sold online labeled 'research use only' or 'not for human consumption' remain subject to FDA intended-use doctrine — marketing or using such products for human therapeutic purposes is unlawful regardless of label. Inclusion here is for educational context only.

Peptides Studied for Immune Support: Individual Profiles

Each compound below has a distinct mechanism, a distinct evidence base, and a distinct regulatory status. Cross-compound comparisons require the caveat that they have been studied in different populations, at different doses, and with different immunological endpoints. Inferring relative effectiveness across separate research programs is not methodologically reliable.

Thymosin alpha-1

Thymosin alpha-1 is a synthetic 28-amino-acid peptide corresponding to the N-terminal sequence of prothymosin alpha, an endogenous thymic protein. Its proposed mechanism for immune support is multifaceted: King and colleagues, reviewing immune modulation with thymosin alpha-1 in Vitamins & Hormones in 2016, reviewed its reported effects on T-cell, dendritic cell, and antibody responses across the immune cascade. Romani and colleagues, writing in the Annals of the New York Academy of Sciences in 2010, described thymosin alpha-1 as a proposed regulator of other immune regulators — framing its role as a coordinator of the immune cascade rather than a simple stimulant. A 2007 paper by Romani and colleagues in the same journal described thymosin alpha-1 as an endogenous regulator of inflammation, immunity, and tolerance, establishing its role as an endogenous immune-regulatory peptide.

Foundational overviews of the compound span two decades: Ancell, writing in the American Journal of Health-System Pharmacy in 2001, provided the primary historical and foundational overview of thymosin alpha-1, and a 2010 review by Li and colleagues in Peptides detailed thymosin alpha-1's biological activities, applications, and production. Goldstein and colleagues, writing in Expert Opinion on Biological Therapy in 2009, reviewed emerging clinical applications of thymosin alpha-1; Tuthill and colleagues in a 2010 Annals of the New York Academy of Sciences paper covered the compound's past clinical experience and future promise.

The largest narrative evidence synthesis in the peer-reviewed literature identified at the time of writing is the review by Dinetz and colleagues published in Alternative Therapies in Health and Medicine in 2024, documenting data on thymosin alpha-1 across more than 30 clinical trials involving over 11,000 human subjects — predominantly in foreign-approval jurisdictions, across hepatitis B, hepatitis C, cancer, and immunodeficiency indications. These trials have not been accepted by FDA as establishing safety and efficacy for any US indication. One example of the evidence landscape's complexity: Binsfeld and colleagues' 2015 paper in Cancer Immunology, Immunotherapy reported that thymosin alpha-1 did not exert anti-myeloma effects in a multiple myeloma stem cell transplantation context — a reminder that aggregated trial counts include studies with null results, and that single-center findings do not establish efficacy in any indication. [Does not constitute an FDA efficacy determination. Among compounds discussed in this article, thymosin alpha-1 has the largest published clinical footprint — predominantly in foreign-approval jurisdictions not accepted by FDA as establishing US safety or efficacy.]

Thymosin alpha-1 is not FDA-approved for any indication in the US. Its use for any indication has not been approved by the FDA; the safety and efficacy for US indications have not been established through FDA-reviewed adequate and well-controlled clinical trials. It is not on the FDA's Section 503A bulk drug substances list and is not currently permitted for compounding under Section 503A. Not currently available through Superpower.

Thymalin

Thymalin is a Khavinson bioregulator derived from bovine thymus tissue. Khavinson and colleagues, publishing in Bulletin of Experimental Biology and Medicine in 2020, documented thymalin's activation of haematopoietic stem cell differentiation as a direct immunological mechanism. The primary human evidence for thymalin as an immune-supporting compound comes from two longitudinal studies conducted in a Russian clinical research context with methodological standards that differ from FDA RCT requirements: Khavinson and colleagues, publishing in 2003, reported findings that thymalin and epithalamin were associated with longer life span during a 6-8 year observation, and a Russian-language study in Advances in Gerontology in 2002 by Khavinson and colleagues reported mortality outcomes in 266 elderly patients in its English abstract. [Human longitudinal data from Russian clinical research; methodological standards differ from FDA Phase 3 RCT requirements] Thymalin is not FDA-approved in the US, does not appear on the FDA's Section 503A bulk drug substances list, and is not lawfully available through US compounding pharmacies; Russian regulatory approval does not confer any US regulatory status. Not currently available through Superpower.

Thymulin

Thymulin is a thymus-origin signaling hormone — a zinc-dependent nonapeptide proposed to promote T-cell maturation. Its clinical relevance as an immune-support target rests on two well-characterized facts: thymulin declines with age as the thymus involutes, and it declines with zinc deficiency because zinc binding is required for bioactivity. Reggiani and colleagues, writing in the Annals of the New York Academy of Sciences in 2009, comprehensively reviewed the thymus-neuroendocrine axis and thymulin's therapeutic potential. Safieh-Garabedian and colleagues' 1992 review in the Journal of Autoimmunity established thymulin's foundational immunomodulatory role. Prasad and colleagues, in a 1988 Journal of Clinical Investigation study, reported that correcting mild zinc deficiency in humans restored serum thymulin activity. [Well-characterized physiology; limited human therapeutic intervention data] Not FDA-approved as a therapeutic; not lawfully available through US compounding pharmacies; therapeutic development at an early preclinical stage.

Prasad and colleagues, writing in the Journal of Nutrition in 2007, reviewed zinc mechanisms of host defense including thymulin-mediated T cell function. Prasad and colleagues, in a 1988 Journal of Clinical Investigation study, reported that correcting mild zinc deficiency in humans restored serum thymulin activity — providing the most practical clinical context: assessing and correcting zinc status is the relevant actionable pathway for thymulin physiology.

LL-37

LL-37 is the only human member of the cathelicidin family, a class of antimicrobial peptides produced by innate immune cells. Scott and colleagues, writing in the Journal of Immunology in 2002, characterized LL-37 as a multifunctional modulator of innate immune responses. Dürr and colleagues, publishing in Biochimica et Biophysica Acta in 2006, established LL-37 as the sole human cathelicidin with broad-spectrum antimicrobial and immunomodulatory properties. Wan and colleagues, writing in the Journal of Innate Immunity in 2014, documented that LL-37 promotes bacterial phagocytosis by human macrophages. Alalwani and colleagues, publishing in the European Journal of Immunology in 2010, showed LL-37 modulates the inflammatory and host defense response of human neutrophils. [In vitro and animal studies only; no completed human clinical trials for therapeutic immune use]

This compound has not been approved by the FDA for any medical use. Research on LL-37 for therapeutic immune support has been limited to laboratory and animal studies, with no completed human clinical trial data. LL-37 is not prescribed, compounded, or dispensed through Superpower. Inclusion is for educational context only.

BPC-157

BPC-157 is a synthetic pentadecapeptide studied primarily for gastrointestinal cytoprotection. Its immune relevance operates through the gut-immune axis rather than direct immunological action. Sikiric and colleagues' 2011 review in Current Pharmaceutical Design surveyed BPC-157's gastrointestinal and systemic biological activity. A 2025 literature-and-patent review by Jozwiak and colleagues in Pharmaceuticals covered BPC-157 multifunctionality across its studied applications. Human immune-specific trial evidence is not available. [Animal studies only for immune applications; no completed human clinical trials]

As of April 2026, BPC-157 is not permitted for compounding under Section 503A following the FDA's February 2026 reclassification, as reflected in the April 2026 bulk drug substances list revisions. FDA has identified significant safety concerns, and BPC-157 is not lawfully available through licensed US compounding pharmacies. BPC-157 is not prescribed or dispensed through Superpower. Inclusion is for educational context only.

Regulatory Status at a Glance

As of April 2026, none of the compounds in this article are FDA-approved for any indication in the US.

• Thymosin alpha-1: Not FDA-approved in the US; has regulatory approvals outside the US that FDA does not recognize; not on the FDA's Section 503A bulk drug substances list and not currently permitted for compounding
• Thymalin: Not FDA-approved in the US; Russian regulatory approval does not confer any US regulatory status; not on the FDA's Section 503A bulk drug substances list and not lawfully available through US compounding pharmacies
• Thymulin: Not FDA-approved as a therapeutic; not lawfully available through US compounding pharmacies; no active US therapeutic development program for exogenous thymulin administration
• LL-37: Not FDA-approved for any indication; no lawful US human-use pathway — a research peptide used in laboratory and preclinical studies
• BPC-157: Not FDA-approved; not permitted for compounding under Section 503A following FDA's February 2026 reclassification, as reflected in the April 2026 bulk drug substances list revisions; FDA has identified significant safety concerns

Compounds without a lawful US human-use pathway are not legal to prescribe, compound, or sell for human use in the US. Mendias and colleagues, in a 2026 review in Sports Medicine, examined the safety and efficacy of approved and unapproved peptide therapies in the context of musculoskeletal injuries and athletic performance, noting that evidence standards vary widely across compounds and that regulatory status is a critical evaluative dimension.

Considerations When Comparing Peptides for Immune Support

Direct comparison between thymosin alpha-1 and the other compounds in this article is complicated by the orders-of-magnitude difference in evidence bases. Thymosin alpha-1 has 30+ clinical trials and 11,000+ human subjects; LL-37 and BPC-157 have no completed human trials for immune applications. These are not comparable evidence tiers, and a provider will make that distinction explicit.

Your specific immune concern: Immunodeficiency, impaired vaccine response, chronic infection susceptibility, age-related immune decline, and gut-mediated systemic inflammation are distinct problems that favor different mechanistic approaches. A provider would characterize the immune concern precisely before discussing any compound.

Existing health conditions and biomarker profile: Zinc deficiency is a commonly identified and directly correctable contributor to impaired thymic immunity (via thymulin). Vitamin D deficiency independently impairs immune regulation. Chronic elevated hs-CRP reflects a systemic inflammatory state that affects immune tone. All three are testable and addressable before any prescription peptide is considered.

Evidence level comfort: Thymosin alpha-1 has Phase 2 and Phase 3 RCT data in human populations with meaningful clinical endpoints. The other compounds in this article do not. A provider will factor this distinction into any discussion.

Regulatory status: Only thymosin alpha-1 and thymalin are accessible through US compounding pharmacies at this time. LL-37 and BPC-157 are not available through licensed prescribers. This is not a nuance — it determines what conversations with a US-licensed provider are legally possible.

This is not an exhaustive list of clinical considerations. A licensed provider will evaluate your full health history, current medications, and baseline lab results before recommending any compound.

Safety Considerations

Safety profiles differ substantially across this compound class. Thymosin alpha-1 has the most extensive human safety data of any compound in this article, arising from 30+ clinical trials. Thymalin has decades of Russian clinical use with some safety reporting. Thymulin, LL-37, and BPC-157 have limited or no published human safety data for therapeutic administration.

Contraindications that apply broadly to immunomodulatory peptide therapy include:

• Active autoimmune disease — compounds that activate T-cell and dendritic cell responses may exacerbate autoimmune conditions; this requires careful provider evaluation; see the peptides for autoimmune disease article for relevant evidence
• Solid organ or stem cell transplantation patients on immunosuppression — immune stimulation could interact with maintenance immunosuppression therapy
• Active malignancy — immunomodulatory effects require oncology provider input in cancer treatment contexts
• Pregnancy and breastfeeding — no reproductive safety data exists for any compound in this category
• Known hypersensitivity to bovine-derived proteins — applies specifically to thymalin, which is bovine-derived

For compound-specific safety profiles, see individual compound pages as the peptides cluster expands.

What to Test Before Starting Peptides for Immune Support

Regardless of which compound you and your provider discuss, baseline biomarker testing establishes the objective starting point. For immune support specifically, testing identifies modifiable contributors — zinc deficiency, vitamin D insufficiency, chronic inflammation — that may be the most directly relevant and addressable factors before any prescription peptide is introduced.

• CBC with differential: Measures white blood cell count and populations including lymphocytes and neutrophils. Why it matters: white blood cell count and differential characterize the baseline abundance and relative proportions of immune cell populations before any intervention.
• hs-CRP: Measures systemic inflammation. Why it matters for immune support: chronic low-grade inflammation is associated with accelerated immunosenescence and may reflect the same immune dysregulation that thymic peptides are proposed to address. High-sensitivity CRP provides the inflammatory reference point for any immunomodulatory intervention.
• Zinc (serum or plasma): Directly relevant to thymulin bioactivity. Why it matters: zinc deficiency impairs thymulin's ability to promote T-cell maturation. Prasad and colleagues, in a 1988 Journal of Clinical Investigation study, reported that correcting mild zinc deficiency in humans restored serum thymulin activity. This is a nutrient-level intervention with well-established evidence that should be assessed before any peptide compound is considered.
• Vitamin D (25-hydroxy): A steroid hormone with modulatory roles in both innate and adaptive immunity. Why it matters: vitamin D deficiency is highly prevalent and independently impairs immune responses, T-cell function, and autoimmune regulation. Superpower's guide on vitamin D and autoimmune conditions covers the immune-regulatory context in detail.
• IGF-1: The primary downstream marker of growth hormone axis activity. Why it matters in the immune context: IGF-1 supports thymic function and immune cell proliferation; age-related decline in IGF-1 is associated with accelerated thymic involution. Measuring IGF-1 levels provides hormonal context for thymic immune discussions.
• Comprehensive metabolic panel (ALT, AST, eGFR): Liver and kidney function. Why it matters: injectable immunomodulatory compounds are processed through hepatic and renal clearance pathways; organ function baseline is standard pre-treatment assessment.

CBC with differential, hs-CRP, zinc, and vitamin D together address the most common modifiable contributors to impaired immune function. Testing immune system biomarkers at baseline creates the reference data that makes any subsequent immune evaluation interpretable.

Regulatory Access Status for These Peptides

Neither thymosin alpha-1 nor thymalin is currently permitted for compounding under FDA Section 503A bulk drug substances rules. A small number of pharmacies may compound these peptides outside the 503A framework; FDA has identified such compounding as falling outside lawful 503A practice, and products from such sources are outside the sterile-compounding quality controls that protect patient safety. No lawful US compounding pathway currently exists for thymosin alpha-1 or thymalin, and patients should not pursue these compounds outside the regulated system. A licensed provider is the only appropriate source for any discussion of immune-support peptide therapy options, and the conversation should include each compound's actual US regulatory status. A provider evaluation for immunomodulatory peptide therapy typically involves characterization of the immune concern, ruling out modifiable contributors, reviewing health history for autoimmune conditions or immunosuppressive medications, and establishing baseline labs.

LL-37 and BPC-157 are not available through licensed US prescribers. LL-37 has no lawful US human-use pathway and is used only in laboratory and preclinical studies. BPC-157 is not permitted for compounding under Section 503A following FDA's February 2026 reclassification (reflected in the April 2026 bulk drug substances list revisions). Products sold online as either compound for therapeutic immune use operate outside FDA oversight and carry contamination, dosing, and identity risks documented in the independent literature on unregulated peptide preparations, including case reports of serious adverse events from self-administered online-purchased peptides (e.g., Peters and colleagues, CEN Case Reports 2020). Under FDA's intended-use doctrine, products labeled "research use only" or "not for human consumption" are not exempt from regulation as drugs if the actual intended use is human therapeutic.

Addressing documented nutrient deficiencies — zinc and vitamin D — is a well-evidenced, low-risk first step with direct immune implications that does not require any prescription compound. A comprehensive baseline assessment that identifies these deficiencies may resolve the immune concern before a peptide discussion is clinically warranted.

Understanding Your Baseline

With five compounds profiled across a wide evidence spectrum, the question of which is relevant for a specific individual's immune health concern cannot be answered without knowing where that individual's immune function, nutrient status, and inflammatory burden currently stand. Zinc deficiency impairing thymulin activity is addressable through zinc repletion. Vitamin D deficiency suppressing immune regulatory function is addressable through supplementation. Elevated hs-CRP reflecting chronic inflammation points toward anti-inflammatory strategies that precede any peptide discussion. Baseline data is what makes those distinctions visible.

That principle is central to Superpower's approach to preventive health. Whether the conversation with your provider leads to nutrient repletion, a compounded immunomodulatory peptide, or a different approach, the starting point is the same: knowing where your biomarkers stand.

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IMPORTANT SAFETY INFORMATION

Thymosin alpha-1 is not approved by the FDA for any indication. It is not on the FDA's Section 503A bulk drug substances list and is not currently permitted for compounding under Section 503A. Its use for any indication has not been approved by the FDA, and the safety and efficacy for US indications have not been established through FDA-reviewed adequate and well-controlled clinical trials. Superpower does not currently offer thymosin alpha-1. Always consult a licensed healthcare provider before initiating any peptide therapy. General precautions include: contraindicated in patients with active autoimmune disease, transplant patients on immunosuppressive therapy, and patients with active malignancy unless under oncology supervision. No reproductive safety data exists.

Thymalin is not approved by the FDA for any indication. Thymalin is derived from bovine thymus tissue — individuals with known allergies to bovine-derived products should discuss this with a provider before use. Thymalin does not appear on the FDA's Section 503A bulk drug substances list and is not lawfully available through US compounding pharmacies. Russian clinical approval does not establish FDA safety or efficacy. Superpower does not currently offer thymalin. Immunomodulatory concern applies in autoimmune, transplant, and active malignancy contexts.

Thymulin as a therapeutic compound is not FDA-approved for any indication and is not lawfully available through US compounding pharmacies. There is no active US therapeutic development program for exogenous thymulin administration. Thymulin is not prescribed, compounded, or dispensed through Superpower at this time. This section is provided for educational purposes only.

LL-37 is not approved by the FDA for any medical use and has no lawful US human-use pathway. Research has been limited to laboratory and animal studies, with no completed human clinical trial data available for therapeutic immune applications. Safety, efficacy, appropriate dosing, and long-term effects in humans have not been established. Under FDA's intended-use doctrine, products labeled "research use only" are not exempt from regulation as drugs if the actual intended use is human therapeutic. LL-37 is not prescribed, compounded, or dispensed through Superpower. This section is provided for educational purposes only and does not constitute medical advice or an endorsement of use.

BPC-157 is not approved by the FDA for any medical use. As of April 2026, BPC-157 is not permitted for compounding under Section 503A following FDA's February 2026 reclassification, as reflected in the April 2026 bulk drug substances list revisions; FDA has identified significant safety concerns. Research for immune applications is limited to animal studies, with no completed human clinical trial data. BPC-157 is not prescribed, compounded, or dispensed through Superpower. This section is provided for educational purposes only.

Full FDA-approved prescribing information for any prescription compound at dailymed.nlm.nih.gov.